1. Field of the Invention
This invention relates to a method for formation of a deposited film which is applied for production of electronic devices such as photoconductive member for electrophotography, electronic devices such as semiconductor devices such as optical input sensor device for optical image inputting device, thin film transistor, etc., and the like.
2. Related Background Art
In the prior art, for amorphous or polycrystalline deposited films to be used for electronic devices such as semiconductor devices, etc., individually suitable film forming methods have been employed from the standpoint of the desired physical characteristics, uses, etc.
For example, for formation of silicon deposited films such as amorphous or polycrystalline non-single crystalline silicon which are optionally compensated for lone pair electrons with a compensating agent such as hydrogen atoms (H) or halogen atoms (X), etc., (hereinafter abbreviated as "NON-Si (H,X)", particularly "A-Si (H,X)" when indicating an amorphous silicon and "poly-Si (H,X)" when indicating a polycrystalline silicon) (the so-called microcrystalline silicon is included within the category of A-Si (H,X) as a matter of course), there have been attempted the vacuum vapor deposition method, the plasma CVD method, the thermal CVD method, the reactive sputtering method, the ion plating method, the optical CVD method, etc. Generally, the plasma CVD method has been widely used and industrialized.
However, the reaction process in formation of a silicon-based deposited film according to the plasma CVD method which has been generalized in the prior art is considerably complicated as compared with the conventional CVD method, and its reaction mechanism involves a great many complex steps. Also, there are a large number of parameters for formation of a deposited film (for example, substrate temperature, flow rate and flow rate ratio of the introduced gases, pressure during formation, high frequency power, electrode structure, structure of the reaction vessel, speed of evacuation, plasma generating system, etc.). By combination of such a large number of parameters, the plasma may sometimes become unstable state, whereby marked deleterious influences were exerted frequently on the deposited film formed. Besides, the parameters characteristic of the device must be selected for each device and therefore under the present situation it has been difficult to generalize the production conditions.
On the other hand, for the silicon-based deposited film to exhibit sufficiently satisfactory electric and optical characteristics for respective uses, it is now accepted that it is form the film according to the plasma CVD method.
However, depending on the application use of the silicon-based deposited film, bulk production with reproducibility must be attempted with full satisfaction of enlargement of area, uniformity of film thickness as well as uniformity of film quality, and therefore in formation of a silicon-based deposited film according to the plasma CVD method, enormous installation investment is required for a bulk production device and also management items for such bulk production becomes complicated, with management being difficult and the control of the device being complex. These are pointed as the problems to be improved in the future.
Also, in the case of the plasma CVD method, since plasma is directly generated by high frequency or microwave, etc., in the film forming space in which a substrate on which film is formed is arranged, electrons or a number of ion species generated may cause damage to the film in the film forming process to cause lowering in film quality or non-uniformization of film quality.
As an improvement of this point, the indirect plasma CVD method has been proposed.
The indirect plasma CVD method has been elaborated to use selectively the effective chemical species for film formation by forming plasma by microwave, etc., at an upstream position apart from the film forming space and transporting the plasma to the film forming space.
However, even by such a plasma CVD method, transport of plasma is essentially required and therefore the chemical species effective for film formation must have long life, whereby the gas species which can be employed are inevitably limited, thus failing to give various deposited films. Also, enormous energy is required for generation of plasma, and generation of the chemical species effective for film formation and their amounts cannot be essentially placed under simple management. Thus, various problems remain to be solved.
As contrasted with the plasma CVD method, the optical CVD method is advantageous in that no ion species or electrons are generated which cause damage to the film quality during film formation. However, there are problems such that the light source does not include so much kinds, that the wavelength of the light source tends to be toward UV-ray side, that a large scale light source and its power source are required in the case of industrialization, that the window for permitting the light from the light source to be introduced into the film forming space is coated with a film during film formation resulting in a lowering in the amount of light during film formation, which may further lead to shut-down of the light from the light source into the film forming space.
Also, in formation of a silicon-based deposited film, for obtaining sufficient device characteristics to stand practical application and also improving yield, it is necessary to clean sufficiently or smoothen the surface of the substrate for formation of a deposited film thereon.
However, before placing the substrate, subjected previously to pre-treatment such as by washing and smoothing the film forming space for formation of a deposited film, the above substrate may be contaminated again or the surface may be damaged, whereby there can be the problem that a deposited film without good device characteristics may be formed.
As described above, in formation of a silicon based deposited film, the points to be solved still remain, and it has been earnestly desired to develop a method for forming a deposited film which is capable of bulk production by attempting to effect energy saving by means of a device of low cost, while maintaining good film characteristics including uniformity to a practical level. These are also applicable for other deposited films such as silicon nitride films, silicon carbide films, silicon oxide films as the similar problems which should be solved respectively.
On the other hand, etching of semiconductor layers in the methods for forming electronic devices of the prior art includes the liquid phase etching (wet etching) and the gas phase etching (dry etching).
The liquid phase etching is carried out by dipping a electronic device into an etching solution with the necessary portion thereof being masked and removing the portion other than the masked portion by etching through the chemical reaction. However, due to insufficient adhesion of the mask and impregnation of the etching solution, there was involved the problem that unnecessary portions were also etched.
On the other hand, the gas phase etching may be typically plasma etching. Particularly, the system in which plasma etching and the sputtering effect are utilized in combination is capable of control of selective etching ratio or anisotropic etching, etc. through the action of the reactive gas and the sputtering action, and therefore it is now becoming predominant as the etching technique for minute working.
However, even in the gas phase etching, masking is also required similarly as in the liquid phase etching, whereby the steps for carrying out patterning and separation of semiconductor layers, etc. are increased and bulk productivity cannot be improved. Also, there was involved the problem that management of film quality was complicated.